ISO/IEC 9594-1:2020

INTERNATIONAL ISO/IEC
STANDARD 9594-1
Ninth edition
2020-11
Information technology — Open
systems interconnection —
Part 1:
The Directory: Overview of concepts,
models and services
Reference number
©
ISO/IEC 2020
© ISO/IEC 2020
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ii © ISO/IEC 2020 – All rights reserved

Foreword
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This document was prepared by ITU-T as ITU-T X.500 (10/2019) and drafted in accordance with
its editorial rules, in collaboration with Joint Technical Committee ISO/IEC JTC 1,
Information technology, Subcommittee SC 6, Telecommunications and information exchange between
systems.
This ninth edition cancels and replaces the eighth edition (ISO/IEC 9594-1:2017), which has been
technically revised.
A list of all parts in the ISO/IEC 9594 series can be found on the ISO website.
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© ISO/IEC 2020 – All rights reserved iii

CONTENTS
Page
1 Scope . 1
2 Normative references. 1
2.1 Identical Recommendations | International Standards . 1
3 Definitions . 2
3.1 Communication model definitions . 2
3.2 Directory model definitions . 2
3.3 Distributed Operation definitions . 3
3.4 Replication definitions . 3
3.5 Basic directory definitions . 3
4 Abbreviations . 3
5 Conventions . 4
6 Overview of the Directory . 4
7 The Directory Information Base (DIB) . 5
8 The Directory service . 7
8.1 Introduction . 7
8.2 Service qualification . 7
8.3 Directory interrogation . 7
8.4 Directory modification . 8
8.5 Other outcomes . 8
9 The distributed Directory . 9
9.1 Functional model . 9
9.2 Organizational model . 9
9.3 Operation of the model . 9
10 Access control in the Directory . 13
11 Service administration . 14
12 Replication in the Directory . 15
12.1 Introduction . 15
12.2 Forms of Directory replication . 15
12.3 Replication and consistency of Directory information . 16
12.4 Views of replication . 16
12.5 Replication and Access Control . 17
13 Directory protocols . 17
Annex A – Applying the Directory . 18
A.1 The Directory environment . 18
A.2 Directory service characteristics . 18
A.3 Patterns of use of the Directory . 18
Annex B – Amendments and corrigenda . 22
© ISO/IEC 2020 – All rights reserved
Rec. ITU-T X.500 (10/2019) v
Introduction
This Recommendation | International Standard together with other Recommendations | International Standards, has been
produced to facilitate the interconnection of information processing systems to provide directory services. A set of such
systems, together with the directory information that they hold, can be viewed as an integrated whole, called the Directory.
The information held by the Directory, collectively known as the Directory Information Base (DIB), is typically used to
facilitate communication between, with or about objects such as application entities, people, terminals and distribution
lists.
The Directory plays a significant role in Open Systems Interconnection, whose aim is to allow, with a minimum of
technical agreement outside of the interconnection standards themselves, the interconnection of information processing
systems:
– from different manufacturers;
– under different managements;
– of different levels of complexity; and
– of different ages.
This Recommendation | International Standard introduces and models the concepts of the Directory and of the DIB and
overviews the services and capabilities which they provide. Other Recommendations | International Standards make use
of these models in defining the abstract service provided by the Directory, and in specifying the protocols through which
this service can be obtained or propagated.
This Recommendation | International Standard provides the foundation frameworks upon which industry profiles can be
defined by other standards groups and industry forums. Many of the features defined as optional in these frameworks,
may be mandated for use in certain environments through profiles. This ninth edition technically revises and enhances,
the eighth edition of this Recommendation | International Standard.
Annex A, which is an integral part of this Recommendation | International Standard, describes the types of use to which
the Directory can be applied.
Annex B, which is not an integral part of this Recommendation | International Standard, lists the amendments and defect
reports that have been incorporated to form this edition of this Recommendation | International Standard.
© ISO/IEC 2020 – All rights reserved
vi Rec. ITU-T X.500 (10/2019)
INTERNATIONAL STANDARD
ITU-T RECOMMENDATION
Information technology – Open Systems Interconnection –
The Directory: Overview of concepts, models and services
1 Scope
The Directory provides the directory capabilities required by many application layer standards and telecommunication
services. Among the capabilities which it provides are those of "user-friendly naming", whereby objects can be referred
to by names which are suitable for citing by human users (though not all objects need have user-friendly names); and
"name-to-address mapping" which allows the binding between objects and their locations to be dynamic. The latter
capability allows networks, for example, to be "self-configuring" in the sense that addition, removal and the changes of
object location do not affect network operation.
The Directory is not intended to be a general-purpose database system, although it may be built on such systems. It is
assumed, for instance, that, as is typical with communication directories, there is a considerably higher frequency of
"queries" than of updates. The rate of updates is expected to be governed by the dynamics of people and organizations,
rather than, for example, the dynamics of networks. There is also no need for instantaneous global commitment of updates;
transient conditions, where both old and new versions of the same information are available, are quite acceptable.
It is a characteristic of the Directory that, except as a consequence of differing access rights or un-propagated updates,
the results of directory queries will not be dependent on the identity or location of the inquirer. This characteristic renders
the Directory unsuitable for some telecommunication applications, for example some types of routing. For cases where
the results are dependent on the identity of the inquirer, access to directory information and updates of the Directory may
be denied.
2 Normative references
The following Recommendations and International Standards contain provisions which, through reference in this text,
constitute provisions of this Recommendation | International Standard. At the time of publication, the editions indicated
were valid. All Recommendations and Standards are subject to revision, and parties to agreements based on this
Recommendation | International Standard are encouraged to investigate the possibility of applying the most recent edition
of the Recommendations and Standards listed below. Members of IEC and ISO maintain registers of currently valid
International Standards. The Telecommunication Standardization Bureau of the ITU maintains a list of currently valid
ITU-T Recommendations.
2.1 Identical Recommendations | International Standards
– Recommendation ITU-T X.200 (1994) | ISO/IEC 7498-1:1994, Information technology – Open Systems
Interconnection – Basic Reference Model: The basic model.
– Recommendation ITU-T X.501 (2019) | ISO/IEC 9594-2:2020, Information technology – Open Systems
Interconnection – The Directory:
...